1. Field of the Invention
The present invention relates to a flexible circuit board microvia technology and in particular to a microvia structure of a flexible circuit board and a manufacturing method thereof, which provide advantages of enlarged conductive contact surface area, reduced impedance, and ensured conduction reliability.
2. The Related Arts
The flexible circuit technology has been widely used in all sorts of electronic equipment, communication equipment, and instruments. To achieve a desired circuit arrangement, it is common to form conductive traces and via structures on and in a flexible circuit board. FIG. 1 is a schematic view that illustrates a conventional via structure formed in a flexible circuit board. The flexible circuit board has a structure that comprises a dielectric layer, a first conductive layer, and a second conductive layer, in which the first conductive layer and the second conductive layer are respectively formed on a first surface and a second surface of the dielectric layer.
To form a via structure in the flexible circuit board, commonly, a through hole is formed in the flexible circuit board and electroplating is applied to for an electroplated layer (such as a copper layer) on a wall of the through hole. Etching is then applied to form the conductive traces so that predetermined ones of the conductive traces of the first and second conductive layers are in electrical connection with each other through the electroplated layer.
The conventional via structure of the flexible circuit board, although fit to the uses of the electronic circuits, no longer satisfies the need of the modern industries when the conductive traces and spacing distances therebetween get smaller and smaller. Further, the via structure that is formed with the known technology involves a large thickness of electroplated copper, which does not suit the need of the modern industries and is adverse to the use of the flexible circuit board.